One Rep Max Calculator

Why we show a range, not one falsely-precise number

Most 1RM calculators return a single number from one formula, or a blend they don't disclose. The most-cited comparative accuracy study in the field — LeSuer et al. (1997), Journal of Strength and Conditioning Research 11(4), 211-213 — directly tested 7 prediction equations against actual measured 1RM in the bench press, squat and deadlift, and found no single formula is universally superior; accuracy depends on the exercise, the rep range, and the lifter's experience. Wikipedia's summary of the comparison literature is blunter still: the formulas “greatly diverge after about 10 reps.” Showing one decimal-precise number hides that documented uncertainty. We show the full 7-formula range plus their average instead, so you can see how much the estimate actually varies.

The 7 formulas, in full — with their original source

Every estimate above comes from one of these seven published prediction equations. Each was derived from a different dataset (bench-press-to-failure trials, NFL Combine-style testing, general strength-training populations), which is exactly why they don't agree perfectly:

Epley (1985) — 1RM = W x (1 + reps/30). Most widely used formula; adds ~3.33% per rep (linear). Accurate 1-10 reps; tends to overestimate above ~10 reps. Identical result to Brzycki at exactly 10 reps. Source: Epley, Boyd (1985). "Poundage Chart." Boyd Epley Workout. Lincoln, NE: Body Enterprises, p.86.

Brzycki (1993) — 1RM = W x 36 / (37 - reps). Widely regarded as most accurate for 1-10 reps; hyperbolic model becomes increasingly conservative as reps rise. Mathematically undefined/unstable as reps approaches 37 -- not usable above roughly 12-15 reps. Source: Brzycki, Matt (1993). "Strength testing -- predicting a one-rep max from reps-to-fatigue." Journal of Physical Education, Recreation & Dance, 64(1), 88-90. https://doi.org/10.1080/07303084.1993.10606684

Lombardi (1989) — 1RM = W x reps^0.10. Power-function model; more conservative than linear formulas (Epley/O'Conner) at higher rep counts. Reasonable 1-10 reps; becomes the most conservative of the 7 formulas by ~12 reps. Source: Lombardi, V.P. (1989). Beginning Weight Training: The Safe and Effective Way. Dubuque, IA: Wm. C. Brown Publishers.

Mayhew et al. (1992) — 1RM = 100 x W / (52.2 + 41.9 x e^(-0.055 x reps)). Developed from NFL Combine-style bench-press-to-failure data (predominantly upper-body pressing movements). Exponential model, reasonably accurate through ~10 reps; may be more exercise-specific to pressing movements than squat/deadlift. Source: Mayhew, J.L., Ball, T.E., Arnold, M.D., Bowen, J.C. (1992). "Relative muscular endurance performance as a predictor of bench press strength in college men and women." Journal of Applied Sport Science Research, 6(4), 200-206.

O'Conner et al. (1989) — 1RM = W x (1 + 0.025 x reps). Most conservative of the common linear formulas (adds only 2.5% per rep vs Epley's 3.33%). Accurate low-rep range; systematically underestimates relative to other formulas as reps increase. Source: O'Conner, B., Simmons, J., O'Shea, P. (1989). Weight Training Today. St. Paul, MN: West Publishing.

Wathan (1994) — 1RM = 100 x W / (48.8 + 53.8 x e^(-0.075 x reps)). Exponential decay model published in the NSCA's core textbook; considered a good balance between the more aggressive Epley and the more conservative O'Conner estimates. Reliable through ~10-12 reps. Source: Wathen, D. (1994). "Load assignment." In T.R. Baechle (Ed.), Essentials of Strength Training and Conditioning (1st ed., pp. 435-446). Champaign, IL: Human Kinetics / NSCA.

Lander (1985) — 1RM = 100 x W / (101.3 - 2.67123 x reps). Simple linear-reciprocal model. Reasonable for moderate rep ranges but becomes unstable/unreliable above ~15 reps as the denominator approaches zero. Source: Lander, J. (1985). "Maximum based on reps." NSCA Journal (National Strength & Conditioning Association Journal), 6(6), 60-61.

How to use the %1RM training-load table

The training-load table pre-fills each rep target (1 to 12) with the weight from the NSCA Training Load Chart (Baechle & Earle, eds., Essentials of Strength Training and Conditioning, 2nd ed., 2000) applied to your average estimated 1RM. For example, if your 5-rep test gives an average estimate of 259.8 lb, the table shows ~87% of that (≈226 lb) as the weight that should let you complete roughly 5 reps to near-failure. Programming for strength generally sits in the 1-5 rep / 80-100% band; hypertrophy in the 8-12 rep / 67-80% band; muscular endurance at 12+ reps / under 67%. The 11-rep row is interpolated (marked with *) — NSCA's official chart has no published 11-rep entry, so we sit it between the official 10-rep (75%) and 12-rep (70%) values, matching the independently-published Bodybuilding.com version of the same table.

Limits: why we stop calculating past 12 reps

These formulas are validated primarily for 1-10 repetitions. Past 10 reps we flag the estimate as lower-confidence, and past 12 reps we don't compute a fresh estimate at all — we show you the 12-rep figure instead, because formula divergence becomes too large to be a meaningful range (per LeSuer 1997 and the Wikipedia comparison chart; one r/GarageStrength discussion among lifters makes the same point — formulas are “most accurate in the 3-5 rep range” and “skewed the farther above 5 reps you get”). They were also derived mainly from experienced lifters doing barbell bench press, squat and deadlift, so accuracy is lower for beginners, machine exercises, or lifts with a large technique component (e.g. Olympic lifts). Treat every number here as a planning estimate, not a target to chase without a spotter.

Safety and scope

• This is a statistical estimate based on published prediction formulas, not a substitute for an actual tested one-repetition maximum.
• Formulas were developed from studies of trained/experienced lifters performing barbell exercises (primarily bench press, squat, deadlift); accuracy may be lower for beginners, novel exercises, or machine-based lifts.
• Never attempt to lift at or near your estimated 1RM without a qualified spotter and proper safety equipment (e.g., a power rack with safety bars).
• Beginners should prioritize learning proper technique before testing or training near maximal loads.
• This tool provides general fitness information and is not medical advice. Consult a physician before beginning any new strength-training program, especially if you have a pre-existing injury or health condition.